I. Field of the Invention
The present invention relates generally to a method for cellular communication. In particular, the invention relates to maximizing data rates in cellular communication systems.
II. Description of the Related Art
Cellular communication systems have experienced tremendous growth in the past few years as the number of wireless end users have increased. Coupled with increased end users, cellular communication use has expanded to a wide array of applications. These applications include the popular wireless telephone use, global position satellite systems and wireless data transfer, e.g. wireless internet or electronic mail access. As the number of end users and types of applications increase, the need to maximize data throughput also increases.
As FIG. 1 shows, in order to serve large geographic areas, cellular communication systems are divided into cells 100, 200, 300 that each encompass particular geographical sections of the service area. A base station 102, 202, 302 is deployed in and is associated with each cell 100, 200, 300. The base stations 102, 202, 302 of various cells 100, 200, 300 are connected by a wireline network 48 and are controlled by a control station 400 using the wireline network 48. The control station 400 provides the necessary computing and communication processing required to manage the network of base stations 102, 202, 302 throughout the service area.
Each base station 102, 202, 302 services all the mobile devices within the cell 100, 200, 300 surrounding the base station 102, 202, 302 with a required radio frequency (RF) signal. RF signal strength for a signal received by a mobile device varies based upon the mobile device's location in the cell and velocity. However, generally, a required RF signal strength (power) is one where the signal to interference ratio (SIR) is within a satisfactory range at the mobile device receiving a downlink signal. (This is also true for a base station 102, 202, 302 receiving an uplink signal.) Such an acceptable range is known to those skilled in the art. An acceptable SIR is one whereby a signal can be received by a mobile device (or by a base station receiving an up link signal) without excessive interference which would require re-transmission or loss of data. We consider here systems, such as CDMA as well as third and later generation systems using other multiple access techniques, in which each mobile device can be allocated a different signal strength, depending upon need. As used herein, “mobile device” is defined as any type of mobile wireless communications device including but not limited to portable cellular telephones; automobile telephones; laptop and palmtop computers and personal digital assistant (PDA) equipment with wireless modems; time division multiple access (TDMA), code division multiple access (CDMA) and general packet radio services (GPRS) transceivers; pagers; and other wireless voice and data communication devices.
The base station 102, 202, 302 in each cell 100, 200, 300 has a number of radio communication channels which it can assign for transmissions within that cell 100, 200, 300 and a finite total available RF signal power the base station 102, 202, 302 can use. The required RF signal power needed for a transmission is an increasing function of the distance a mobile device is from the base station 102, 202, 302. Therefore, for the same data transfer rate, a mobile device closer to a base station 102, 202, 302 will require less power in terms of RF signal power than a mobile device more distant from a base station 102, 202, 302. When mobile devices are closer to their respective base station 102, 202, 302 of the cell 100, 200, 300, base station power is conserved. With this conserved power each base station can: (a) service more mobile devices within a cell 100, 200, 300, assuming the respective base station 102, 202, 302 has additional communication channels available, thereby increasing overall system throughput or (b) increase the data rate for a particular mobile device which includes increasing the signal power allocated for that mobile device, assuming the base station 102, 202, 302 and the mobile device can switch to a common protocol which allows for faster data transmission.
The individual cells 100, 200, 300 tile the entire geographical service area. However, the tiling is not exact and neighboring cells 100, 200, 300 normally overlap at handoff regions. (A handoff region is not always a static region and can be variable. Further, a handoff region does not usually occur exactly at a geometric cell border, but rather is based upon RF signal conditions and is affected by factors such as log-normal shadowing and terrain.)
According to conventional practice, when a mobile device crosses the boundary of the current cell, i.e. 100, and moves into another cell, i.e. 200, while transmitting information, a communication path must be established with a new base station 202 located in the new cell 200. If a radio communication channel is not available in the new cell 200 and the mobile device is not able to acquire a new channel in the new cell 200 before it crosses over the boundary and moves completely into the new cell 200, a handoff failure will occur and a transmission in progress will be aborted and, in the case of a pure data transmission, the data must be re-sent once connectivity to the new cell 200 is established. A transmission failure can also occur even if a communication channel is available but the new cell 200 does not have enough remaining RF signal power to support the mobile device in question. The probability of handoff failure, that is, the probability that a transmission in progress will be forcibly aborted during a handoff is a major concern in cellular systems. Handoff failure equates to decreased throughput in mobile devices particularly for data transmission, as the data must be re-sent. Thus, there is a need for a cellular system, which efficiently allocates base station RF signal power, in order to increase individual mobile device data throughput and increase overall network throughput by decreasing data transmission errors and handoff failures, by transmitting to the individual mobile devices when the possibility of transmission and/or handoff failures for each mobile device is minimal.